lundi 10 décembre 2018

Thread's ThreadLocals cleaning

here I have found the following code how to clean Thread's ThreadLocals in Java:

private void cleanThreadLocals() {
    try {
        // Get a reference to the thread locals table of the current thread
        Thread thread = Thread.currentThread();
        Field threadLocalsField = Thread.class.getDeclaredField("threadLocals");
        threadLocalsField.setAccessible(true);
        Object threadLocalTable = threadLocalsField.get(thread);

        // Get a reference to the array holding the thread local variables inside the
        // ThreadLocalMap of the current thread
        Class threadLocalMapClass = Class.forName("java.lang.ThreadLocal$ThreadLocalMap");
        Field tableField = threadLocalMapClass.getDeclaredField("table");
        tableField.setAccessible(true);
        Object table = tableField.get(threadLocalTable);

        // The key to the ThreadLocalMap is a WeakReference object. The referent field of this object
        // is a reference to the actual ThreadLocal variable
        Field referentField = Reference.class.getDeclaredField("referent");
        referentField.setAccessible(true);

        for (int i=0; i < Array.getLength(table); i++) {
            // Each entry in the table array of ThreadLocalMap is an Entry object
            // representing the thread local reference and its value
            Object entry = Array.get(table, i);
            if (entry != null) {
                // Get a reference to the thread local object and remove it from the table
                ThreadLocal threadLocal = (ThreadLocal)referentField.get(entry);
                threadLocal.remove();
            }
        }
    } catch(Exception e) {
        // We will tolerate an exception here and just log it
        throw new IllegalStateException(e);
    }
}

It is quite complicated. What about following simpler code, is it sufficient to clean ThreadLocals? Thank you.

private void cleanThreadLocals(Thread thread) {
    try {
        // Get a reference to the thread locals table of the current thread
        Thread thread = Thread.currentThread();
        Field threadLocalsField = Thread.class.getDeclaredField("threadLocals");
        threadLocalsField.setAccessible(true);
        threadLocalsField.set(thread, null);
    } catch (Exception e) {
        throw new RuntimeException(e);
    }
}





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